Surfactants for enhanced oil recovery

Abstract

Surfactant compositions useful for oil recovery are disclosed. The compositions comprise from 10 to 80 wt. % of a propoxylated C 12 -C 20 alcohol sulfate, from 10 to 80 wt. % of a C 12 -C 20 internal olefin sulfonate, and from 0.1 to 10 wt. % of an ethoxylated C 4 -C 12 alcohol sulfate. Surprisingly, including a minor proportion of the ethoxylated alcohol sulfate reduces or eliminates the need to rely on costly cosolvents for achieving good performance in enhanced oil recovery processes. In particular, low interfacial tensions and low microemulsion viscosities can be achieved when the ethoxylated alcohol sulfate accompanies the propoxylated alcohol sulfate and internal olefin sulfonate. Aqueous concentrates comprising water and the surfactant compositions described above are also disclosed. Dilution of the surfactant composition or aqueous concentrate with water or brine to the desired anionic actives level provides an injectable composition useful for EOR applications. Stable, low-viscosity oil-in-water microemulsions comprising crude oil, water, and the surfactant compositions are also disclosed.

We claim: 
     
       1. A surfactant composition, useful for enhanced oil recovery, comprising:
 (a) from 10 to 80 wt. % of a propoxylated C 12 -C 14  alcohol sulfate having an average of 6 to 8 oxypropylene units or a C 16 -C 18  alcohol sulfate having an average of 6 to 8 oxypropylene units; 
 (b) from 10 to 80 wt. % of a C 15 -C 18  internal olefin sulfonate; and 
 (c) from 1 to 5 wt. % of an ethoxylated C 6 -C 10  alcohol sulfate having an average of 2 to 6 oxyethylene units. 
 
     
     
       2. The composition of  claim 1  comprising from 10 to 40 wt. % of the propoxylated alcohol sulfate and from 50 to 80 wt. % of the internal olefin sulfonate. 
     
     
       3. The composition of  claim 1  comprising from 20 to 30 wt. % of the propoxylated alcohol sulfate, from 60 to 75 wt. % of the internal olefin sulfonate, and from 2 to 4 wt. % of the ethoxylated alcohol sulfate. 
     
     
       4. An aqueous concentrate useful for oil recovery, comprising:
 (a) water; and 
 (b) the surfactant composition of  claim 1 . 
 
     
     
       5. The concentrate of  claim 4  comprising from 15 to 85 wt. % water, from 15 to 85 wt. % of the surfactant composition, and from 0 to 50 wt. % of one or more additives selected from the group consisting of co-surfactants, cosolvents, polymers, alkali compounds, oxygen scavengers, and mixtures thereof. 
     
     
       6. An injectable product made by diluting the surfactant composition of  claim 1  with water or brine to a total anionic actives level within the range of 0.01 to 5 wt. %. 
     
     
       7. An injectable product made by diluting the concentrate of  claim 4  with water or brine to a total anionic actives level within the range of 0.01 to 5 wt. %. 
     
     
       8. A stable, low-viscosity oil-in-water microemulsion comprising crude oil, water, and the surfactant composition of  claim 1 . 
     
     
       9. A surfactant composition, useful for enhanced oil recovery, comprising:
 (a) from 10 to 40 wt. % of a propoxylated C 12 -C 14  alcohol sulfate having an average of 6 to 8 oxypropylene units or a C 16 -C 18  alcohol sulfate having an average of 6 to 8 oxypropylene units; 
 (b) from 50 to 80 wt. % of a C 15 -C 18  internal olefin sulfonate; and 
 (c) from 1 to 5 wt. % of an ethoxylated C 6 -C 10  alcohol sulfate having an average of 2 to 6 oxyethylene units.